Embarking/disembarking devices often have an extension, in the case of a linear displacement what is known as a sliding step, which can be moved back and forth between a retracted and an extended position and for example in an extended position defines a region which can be walked or driven on. These sliding steps often have lateral guides of the extension for fastening to a carriage body or vehicle frame of the vehicle.
Extensions are used in order to help persons to enter and exit a passenger-carrying vehicle by bridging the gap between the vehicle and the embarking/disembarking platform edge, such as the railway platform edge. However, there are problems if the horizontal gap width varies, if there are obstacles there and if forces act on the extension counter to its extension direction. In the extended position, there is the problem that external forces cause the extension to become misaligned. Although the gearing mechanism driving the extension can be made self-limiting, such a force effect can easily result in destruction of the gearing mechanism. In particular, the belt drives, which are desirable owing to their small volume and quiet operation, are particularly susceptible, as such stress can result in longitudinal stretching of the belt. Furthermore, braking of the extension during its movement is desirable as, owing to the desirably high extension and retraction speed, the impact of the extension against an obstacle can result in damage, in particular personal injury.